The application relates generally to cellulose-reinforced composites and, more particularly, to a cellulosic, inorganic-filled plastic composite.
There is a very high demand for wood products. Although wood is a renewable resource, it takes many years for trees to mature. Consequently, the supply of wood suitable for use in construction is decreasing. Therefore, there is a need to develop alternatives to the use of wood in construction.
Cellulosic materials, such as wood fiber, wood flour, sawdust, rice hulls, peanut shells, and the like, have long been added to thermoplastic compounds to achieve a wood-like composite providing reinforcement, reduced coefficient of expansion, and cost reduction. Process methods have been developed to enable blends containing materials having low bulk density (i.e., powders) and poor flow characteristics to be fed at commercially acceptable rates. Blends of this type can be extruded through dies of the appropriate configuration to produce building product type shapes previously made from wood. For example, U.S. Pat. Nos. 3,908,902, 4,091,153, 4,686,251, 4,708,623, 5,002,713, 5,055,247, 5,087,400, and 5,151,238 relate to processes for producing wood-like composites.
A major limitation of cellulosic fillers is the moisture sensitivity of cellulose fibers. This moisture sensitivity may require predrying of the cellulose fibers and the maintenance of low moisture conditions at the time of thermoplastic processing, particularly for cellulose in powder form. In addition, the moisture sensitivity of the cellulose fibers requires the exercise of special care during extrusion to ensure cellulosic encapsulation and/or protection against moisture absorption to avoid moisture deterioration of the cellulosic fibers. Furthermore, the extrusion process can cause thermal degradation of the cellulose fibers.
In light of these shortcomings, there is a need for a cellulosic composite with improved moisture resistance characteristics. Another need exists for a cellulosic composite that is less susceptible to thermal degradation. A need also exists for an improved cellulosic composite that includes inorganic fillers. Yet another need exists for a cellulosic, inorganic-filled composite that can be used as a substitute for natural wood, particle board, wafer board, and the like.
The present invention satisfies some or all of these needs. One embodiment of the present invention is a cellulosic, inorganic-filled plastic composite. The composite is comprised of cellulosic material, talc, and polyethylene. More particularly, the cellulosic material accounts for about 30% to about 70% by weight of the composite, the talc is about 1% to about 20% by weight of the composite, and the polyethylene is about 25% to about 40% by weight of the composite.
The present invention also includes an extruded article that is produced by extruding the aforementioned cellulosic, inorganic-filled plastic composite. The composite used to make the extruded article may include any of the optional or preferred features of the above-described composite.
Another embodiment of the present invention is a method of extruding a cellulosic, inorganic-filled plastic composite profile. The method comprises introducing a cellulosic, inorganic-filled plastic composite into an extruder. The composite may possess any of the optional or preferred features of the above-described cellulosic, inorganic-filled plastic composite. The composite is then melted and extruded through a profile die to form a profile. The profile is then cooled to achieve a final net shape.
In addition to the novel features and advantages mentioned above, other objects and advantages of the present invention will be readily apparent from the following description of the preferred embodiments.